Subnotebook

Subnotebook (also called an ultraportable, superportable or mini notebook) was a marketing term for laptop computers that are smaller and lighter than a typical 'notebook' sized laptop. 
Types and sizes.
As typical laptop sizes have decreased over the course of the 2010s, and other distinguishing features have become mainstream, the distinction between regular-size and 'subnotebook' laptops has largely disappeared; after release of laptops with narrow screen borders the divide of classes can be defined over the 13" machines, but that still a conditional boundary. Prior to this convergence, subnotebooks were also distinguished from netbooks and ultra-mobile PCs, based on both size and market position. 
Classic subnotebooks were smaller than full sized laptops but larger than handheld computers. They were distinguished by smaller screens and bodies and lighter weights relative to contemporaneous laptops. The savings in size and weight were usually achieved partly by omitting ports, and these were typically the first machines to omit optical disc drives (or on some of the earliest models, floppy drives), but they were also some of the first systems which could be paired with docking stations to compensate. The notable form-factor of a subnotebook-oriented docks was a "slice docks" — the more transportable version of classic docking station.
History.
Before 1992.
As first known officialy released high-portable laptop can be mentioned the Tandy model TRS-80 200 from a 1984 with only weight, but with only 8-bit Intel 80C85 CPU and with primitive screen configuration (240 x 128 LCD with 40 X 16 text symbols support). Smaller DOS-based PCs such as the Poqet PC and the Atari Portfolio—both released in 1989—were called either "pocket PCs" or handhelds. 
The Compaq LTE, launched in 1989, was the first to be widely known as a "notebook computer" because its relatively small dimensions — 48 × 220 × 280 mm (1.9 × 8.5 × 11 inches) — matched those of a pair of stacked US Letter (similar to A4) size paper notebooks. In 1990 the Compaq release was followed by IBM PS/2 note and PS/55note lines (later, in October 1992 they was replaced by the very popular IBM ThinkPad, which was the first to include a 10.4" diagonal (8.3" x 6.2" outline) screen in a notebook measuring 56 × 211 × 284 mm (2.2 × 8.3 × 11.7 inches)), and by the relatively compact Sharp PC-6220 model with only weight. For this time portables with noticeably smaller form factors sometimes referred as subnotebooks. The term was also applied to the NEC UltraLite, unveiled in 1988 — although its dimensions (1.4" × 8.3" × 11.75") were very similar to the Compaq LTE, but NEC measuring a significant less weight (typically ). In 1991 the another relatively compact notebooks were released: the PowerBook 100 by Apple—still bulky and heavy machine that measuring 1.8 × 8.5 × 11 inches and weighing , and HP 95LX — compact handheld PC with limited functionality, but only 0.3 kg weight, from other hand.
1992–1995.
In the end of 1992 the PCMag magazine branded two actual models as subnotebooks: this was a Gateway Handbook, originally released in 1992 and updated to use a 486 processor in late 1993 (these model was only 1.6 × 5.9 × 9.7 inches (41 × 150 × 246 mm) and weighed less than three pounds (1.4 kg)) and Dell 320SLi laptop with weight; and later another true subnotebook was released in this year: the Olivetti Quaderno has been produced in Italy, had a compact 32 x 148 × 210 mm case and was only 1.05 kg weight. At the same time the more regular laptop lines reduced their dimensions, for example, the Apple new PowerBook Duo series, which further reduced their notebook line to 1.4 × 8.5 × 10.9 inches (with weight), and Compaq upgraded LTE series with Lite model with 1.8 x 8.5 x 11 in size (this model still weight , but had a color screen); and both lines supporting few on-board features, but which could be inserted into a docking station to achieve the full functionality of a desktop – a succession feature of IBM PS/2 note docking station predecessor (IBM Communications Cartridge) and soon emulated by other manufacturers.
Another early subnotebook was the Hewlett-Packard OmniBook 300, which was launched as a "superportable" in 1993. It measured 1.4 × 6.4 × 11.1 inches, weighed and was available with an optional Flash memory disk instead of a hard drive, to reduce the weight.
Toshiba, which had concentrated on portables in the 1980s, also entered the market that year with the Portege T3400, claiming that "It's the first subnotebook computer with all the functionality of a much larger computer". The version with an 8.4″ monochrome screen measured just 1.7 × 7.9 × 9.8 inches and weighed 1.8 kg. Toshiba also introduced the T3400CT at this time which was the first subnotebook with a color screen.
Then Toshiba really put the subnotebook PC format on the map in 1995 with the Libretto 20. This featured a 6.1″ screen and 270 MB hard disk. CNet reported about the Libretto 50CT that "[it] is the first full-fledged Windows 95 notebook in the United States weighing less than two pounds".
IBM released a Palm Top PC (handheld laptop with 4.7" screen) in 1995.
Compaq introduced its own short lived subnotebook line in 1994 called Contura Aero, which had two models: the greyscale display 4/25 and the color 4/33, notable for using a battery which was intended to be standard rather than only useful for Compaq products.
1996–2000.
IBM had sold "thin and light" models in its ThinkPad range, such as the ThinkPad 560 ultraportable (1996) and best-selling ThinkPad 600 (1998). It finally entered the subnotebook market in 1999 with the 1.3 kg ThinkPad 240, targeted at business travellers. The 240 and 240X had 10.4″ screens. Later, however, IBM replaced these with the X range, with 12.1″ screens. At 8.3″ × 10.6″, the ThinkPad X40 is not much smaller than A4 (8.3″ by 11.7″) and better described as an ultraportable, rather than a subnotebook. But more compact and affordable IBM WorkPad z50 (thin client with 8.2" screen, released in 1999) don't get a market success.
In 1997 Mitsubishi Electric released ultra-compact 12.1" Mitsubishi Pedion laptop line with ultrathin magnesium case (18 × 218 × 297 mm) and chiclet keyboard. This short-living model line was sold only in Japan and discontinued after some hardware issues. Sony launched an ultraportable (ultrathin) less than an inch thick in Japan - the PCG-505, which reached the US in 1997 as the VAIO 505GX. This was followed by the even thinner Sony VAIO X505, which measured just 0.8 × 8.2 × 10.2 inches, and reached 0.3″ at its thinnest. However, it was very expensive and had poor battery life, and was soon withdrawn. Apple replace the aging PowerBook Duo line with relatively light-weight () but short-lived PowerBook 2400c; this was co-designed by IBM and made for Apple by IBM Japan. However, it measured 1.9 × 8.5 × 10.5 inches (48 × 220 × 270 mm), so it was actually bigger than a Compaq LTE notebook, and can be compared with next-year 13" Compaq Armada 3500 with the same weight, but with larger screen and thinner case. In 2000 Compaq released a more compact successor of Digital HiNote line - the 10.3" Armada M300, with magnesium case and 1.6 kg weight.
Sony also launched the C1 range of subnotebooks, starting in Japan in 1998.
2001–2006.
This era notable with split of Intel x86 architectures: the conservative Pentium M-based Intel Centrino mobile platform (with similar to Pentium III CPU energy-effective architecture and with integrated wireless options) and innovative Pentium IV for desktops with high power consumption.
One of the most notable Sony models was the Transmeta-based Vaio PCG-C1VE or PictureBook (2001), which measured only 1×6×9.8 inches. It had a digital camera built into the lid, which could be used for video conferencing or swivelled round to photograph a scene.
This was followed in 2005 by the Transmeta-based Flybook convertible with a touch-sensitive 8.9 inch. screen from Taiwan's Dialogue Technology (Later models used Intel ULV processors.) The Flybook features a built-in phone connection for GPRS or 3G networking, and is available in a range of bright colors. This attracted the attention of non-computer magazines including GQ, FHM, Elle and Rolling Stone. Dimensions of 9.3″ × 6.1″ put the original Flybook A33i on a par with the Libretto, but styled to appeal more to fashion models than computer geeks.
In 2006, Microsoft stimulated a new round of subnotebook development with the UMPC or ultra-mobile PC format code-named Origami. These are basically small versions of Tablet PC computers, which originally shipped with the Microsoft Windows XP Tablet PC Edition 2005. An example is the Samsung Q1.
2007–present.
This era notable with split of Intel mobile x86 processor lines for different usecases:
Another notable implementation was a migrate from CCFL screen backlit to more energy-efficiently and compact LED-backlit screens. On the other hand, over the course of the 2010s, with growing of sales for mainstream users, optical drives and legacy ports became uncommon, and some classic subnotebook features (like additional replaceable batteries, alternative input methods, docking options, Smart Cards, mobile broadband modules, additional storage) become rare. At Computex 2011 Intel announced a new system branding called Ultrabooks; these very much match the prior description of subnotebooks - they used lower-powered processors (but not as low-end as netbooks) and with each generation of Intel processors, the lower-powered U-series processors became a larger part of mainstream sales. typically lacked optical drives and legacy ports, and were generally compact, but as marketed the two terms were rarely used together. Noticeable releases:
In 2007 the ASUS Eee PC became the first of a new class of low-cost laptops commonly called netbooks. Netbooks are typically based upon the Atom processors, while other subnotebooks use more powerful processors such as ULV types.
In 2008, Apple introduced the MacBook Air, which the company claimed was the world's thinnest notebook. This laptop offers a 13.3" LED-backlit display that's instant-on. It also includes a built-in iSight camera, a full-sized, backlit keyboard and a "trackpad"-branded touchpad with support for multi-touch gestures. However, the MacBook Air offers no built-in optical drive. The latest iteration of the MacBook Air weighs 2.96 pounds (1.35 kg).
In the same year Lenovo released last widely known hi-end 12" subnotebook line without touchpad and with optional ordering without webcam; that's was a ThinkPad X200, X200s and X200 Tablet models. Next facelifted generation has a touchpad in a base config. 
In 2010 Dell release a Latitude 2100, Lenovo release a ThinkPad x100e, and HP release a ProBook Education Edition - semi-rugged low-end subnotebooks for education market with laptop charging trolley support. 
In 2011 was released a first chromebook. 
In 2017 HP and ASUS released an ARM-based ultraportables; but the ARM-based non-chromebook laptops were rare from up to end of 2020.