flash eprom

Cambridge Z88

The Cambridge Computer Z88 was an A4-size, lightweight, portable Z80-based computer with a built-in combined word processing/spreadsheet/database application called PipeDream, along with several other applications and utilities, such as a Z80-version of the BBC BASIC programming language.

The Z88 evolved from Sir Clive Sinclair's Pandora portable computer project which had been under development at Sinclair Research during the mid-1980s. After Sinclair Research's existing computer business and the Sinclair brand were sold to Amstrad in 1986, a new company, Cambridge Computer Ltd., was formed to continue development. The Z88 was launched at the Which Computer? Show on February 17, 1987.

Technical description

The Z88 is a portable computer based on a low-power CMOS version of the popular Z80 microprocessor. It comes with 32 KiB of internal pseudo-static RAM and 128 KiB of ROM containing the operating system (called OZ), but can be expanded up to 3.5 MiB of RAM, of which the contents are preserved thanks to the batteries. An integrated capacitor prevents the Z88 from losing its data for a limited amount of time while changing the batteries.

Despite the lightness of the Z88—it weighs 0.9 kg—its construction is surprisingly robust, including its membrane/chiclet keyboard which is both comfortable and almost inaudible (an optional electronic "click" can be turned on if it proves too quiet for the user's taste).

Powered by four AA batteries (giving up to 20 hours of use), the computer has three memory slots; each of which can be used for RAM expansion, removable mass storage, and proprietary program use. Since the slots use RAM, EPROM and ROM for their data transfer, the transfer speeds are usually very high. Although RAM cards of up to 1 MiB capacity were available, they were expensive. Most users used one or two 128 KiB cards.

Though the super-twisted LCD display has only eight lines, it is clear and surprisingly effective. In PipeDream, a miniature view of a whole page appears to the right of the display, giving a good feel for the overall layout, and compensating for the inevitable "letterbox" effect.

Memory map

The 64 KBytes addresables by the Z80 processor are divided in four banks of 16 Kbytes each one. The 4 Mbytes of maximum memory for the system are also divided in 256 segments of 16 Kbytes each one. The hardware can map any of the 16 Kbyte blocks in any of the four banks. The first 512 Kbytes are reserved for ROM; the next 512 Kbytes block are reserved for internal RAM. The next three Mbytes are assigned to each one of the three memory slots.

Current status

The Z88 had something of a cult following, and is still used by a few enthusiasts. A variety of software is available including games and utilities. Since 1998, a 1 MiB Flash EPROM is available which provides convenient non-volatile storage. Once written to the card, files are safe and not reliant on a power supply. Unlike traditional UV EPROM cards (erased with an external UV light), this one can be electrically erased in the slot the computer. The first generation of card only worked in slot 3 where a 12V signal (Vpp) is available. The later generation is based on AMD chips and runs with 5V for erasure. It is possible to read, write and erase flash cards in the three slots and the internal one.

It is also possible for an experienced user to replace the built-in 32 KiB RAM chip with a bigger 128 or 512 KiB static RAM chip. However, the latter requires some extra board modifications, and 512 KiB is the biggest size that can be addressed by the Z88 for the internal RAM. A same modification is possible for the internal EPROM slot. A 512 KiB flash EPROM chip can replace the original ROM. This allows an easy upgrade of the operating system.

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