The IBM PS/1 is a brand for a line of personal computers that marked IBM's return to the home market in 1990, five years after the IBM PCjr. It was replaced by the IBM Aptiva in September 1994. Position among IBM's PC brands The PS/1 line was created for new computer users and was sold in consumer electronics stores alongside comparable offerings from Compaq, Hewlett-Packard, Packard Bell, and others. American PS/1 models came with a modem installed so users could access online IBM help services, which were provided by partnerships with Prodigy and Quantum. Like the PCjr, the PS/1's name suggested a more limited machine than IBM's business line, the PS/2. However, unlike the PS/2, the PS/1 was based upon architecture closer to the AT and compatibles, for example using ISA, plain VGA, and IDE. Although the first models used custom-designed components and design, later desktop and tower models used mostly standard components. The earlier models included a ROM with IBM's PC DOS and a graphical shell, however the system was compatible with other DOS implementations and the shell could be installed on the hard drive. Later models included a feature called "Rapid Resume" which gave the computers the ability to go into standby mode as well as a hibernation function. There were several form factors used during the PS/1's production, with the 2133 and 2155 cases used for several model years while the 2168 tower case was offered later in later models of the PS/1 lineup: 2011 Proprietary design, power supply is within CRT 2121 Proprietary design, power supply is within CRT, up to two available ISA slots 2123 Limited-production model. Based on IBM PS/2 model 30 case, three available ISA slots 2133 Desktop case. The 3x3 references the available slots and drive bays. 2155 Desktop case larger than 2133. The 5x5 references the available slots and drive bays. Including a 5.25" bay. 2168 Tower unit. The 6x8 references the available slots and bays. Including 5.25" bays. Models Models 2011 and 2121 The original PS/1 (Model 2011), based on a 10 MHz Intel 80286 CPU, was designed to be easy to set up and use. It featured 512 KB of on-board memory (expandable to 1 MB or 2.5 MB with proprietary memory modules), built-in modem (in American models only) and an optional 30 MB or 40 MB hard disk. IBM also released a 5.25" disk drive unit, a $169