Pocket-sized computer

Pocket-sized computer describes the post-programmable calculator / pre-smartphone pocket-sized portable-office hardware devices that included the earlier DOS-based palmtops and subsequent Windows-CE handhelds, as well as a few other terms, primarily covering the 1980s through 2007.
Sometimes called Pocket-sized computing devices, they were a series of internally different devices, and included "Handheld" ("Pocket-sized handheld computing device"), and the earlier-introduced "Palmtop"
("Pocket-sized palmtop computing device") and "pocket-sized palmtop computer." The New York Times used the term "palmtop/handheld."
The media called "the first computer that fits in your palm and weighs less than a pound" and its early day competitors a palmtop. Although the word "handheld" was used before Microsoft's 1996 introduction of Windows CE, a lawsuit by Palm, Inc pushed Microsoft's use of the new term Handheld PC.
By 2007, the iPhone began to replace prior portable office devices, and by a decade later there were indications that "SmartGlasses" might be "their" replacement.
Timeline summary.
Neither the Palmtop PC nor the Handheld PC were pocket computers. As late as March 1981 a "computer small enough to fit in a coat pocket" had yet to be introduced.
Market acceptance.
The first hand-held device compatible with desktop IBM personal computers of the time was the DIP Pocket PC aka Atari Portfolio in 1989. The term "Handheld PC" described the product first introduced in 1989 by Atari as "the first computer that fits in your palm and weighs less than a pound." The full version of the ad ran as eight pages and showed the device in actual size, including one page topped by a hand placing an Atari Portfolio(tm) into a suit inner lapel pocket.
Other early models were the Poqet PC of 1989 and the Hewlett Packard HP 95LX of 1991. Other DOS-compatible hand-held computers also existed. Some handheld PCs use Microsoft's Windows CE operating system, with the term also covering Windows CE devices released by the broader commercial market.
Despite the arrival in the early 2010s of devices lacking keyboards, demand for used pocket computers remained strong. The PsiXpda Ultimate Pocket Computer from 2009; the GPD Win from 2016; the Gemini from 2018 and the eponymous GPD Pocket commercial offerings continue to supply this market while the crowd-funded open source hardware Pandora and Pyra maintain small-scale production and ongoing development.
A combination of price and size makes them useful both for business and education; they also target the "games" market.
Nomenclature.
By the mid 1990s, the New York Times referred to these portable office devices as:
Pocket computer was another term used. Subsequently, another publisher's"10 awesome handheld computers from yesteryear" included "1991 - HP 95LX pocket computer" even though HP called it a palmtop and HPmueum called it a handheld PC. As recently as 2017, these terms were intermixed.
Comparison among alternatives.
Early Palmtops, beginning with 
Atari's 1989 Portfolio, used Intel-compatible x86 processors and a mostly IBM-compatible PC architecture and BIOS. Their operating system was DOS-like.
By the late-1990s, non-Intel processors and other operating systems were used for some devices, using Microsoft's Windows CE operating system, even as the term Handheld was growing.
The term PC was helpful, since many Palmtop PCs and Handheld PCs came with some personal-computer, PDA and office applications pre-installed in ROM, and most of them could also run generic, off-the-shelf PC software with minimal if any modifications. Some could also run other operating systems such as GEOS, MINIX 2.0, Windows 1.0-3.0 (in Real mode only), or Linux
Most palmtop PCs were based on a static hardware design for low power consumption and instant-on/off without a need to reboot. Depending on the model, the battery could power the device from several hours up to several days while running, or between a week and a year in standby mode. Combined with the instant-on/off feature, a battery would typically last from a week up to several months in practical use as PDA.
Handheld computer, Palm PC, Palmtop and Personal Digital Assistant (PDA) were used concurrently and almost interchangeably. to describe these pocket-sized computing devices. The acronym PIM referred to Personal Information Manager, a similar type of device that often came with a stylus interface instead of a keyboard. None of these, at the time, were intended to replace the PC.
Non-Wintel (Palm-top/Palm-size/Pocket computer).
Not all of the pocket-sized hardware was/is used for Windows/Intel systems.
At one point the Windows CE market share was less than 10%. Terms used included:
Not all Windows-running devices had a keyboard. If they matched all of the hardware requirements except for lacking a keyboard they were known as:
A list of handheld/pocket Linux computers.
Some of them ran/run Linux.
History.
Each term had a role:
Palmtop PC.
Palmtop PCs from 1989 through 1996 included:
Handheld PC.
The Handheld PC was a late 1990s hardware design for personal digital assistant (PDA) devices running Windows CE. It provided the appointment calendar functions usual for any PDA.
The intent of Windows CE was to provide an environment for applications compatible with the Microsoft Windows operating system, on processors better suited to low-power operation in a portable device.
Originally announced in 1996, the Handheld PC was distinct from the Palm-size, Pocket PC, or smartphone in that the specification provided for larger screen sizes as well as a keyboard.
Personal Digital Assistant (PDA).
Psion's 1984-introduced handheld palmtop device was the first Personal Digital Assistant (PDA). Two years later the Psion Organizer
 was followed by the Psion Organizer II and other pocket-sized computers.
Other, less expensive devices of this type were Palm Inc's Palm Pilot and various Pocket PCs running Windows CE. Their main era was the 1990s, and included the Apple Newton.
Personal Information Manager (PIM).
Both by goal and by marketing, the audience for the "Personal Information Manager (PIM)" was the individual, not the corporation. Market research showed that people "wanted a device that would straddle the telephone and computer."
Until the smartphones of the 2010s, the goal of what an AT&T study called "an intelligent cellphone" was still pending.