Commodore's RAM Expansion Unit (REU) range of external RAM add-ons for their Commodore 64/128 home computers was announced at the same time as the C128. The REUs came in three models, initially the 1700 (128 KB) and 1750 (512 KB), and later the 1764 (256 KB, for the C64). Commodore is the commonly used name for Commodore International, a West Chester, Pennsylvania based electronics company who was a major player in the 1980s home computer field. ... Different types of RAM. From top to bottom: DIP, SIPP, SIMM 30 pin, SIMM 72 pin, DIMM, RIMM RAM redirects here. ... The Commodore 64 (C64, CBM 64) was a popular home computer of the 1980s. ... The Commodore 128 is a home/personal computer, also known as the C128. ... The home computer is a consumer-friendly word for the second generation of microcomputers (the technical term that was previously used), entering the market in 1977 and becoming common during the 1980s. ... A kilobyte (derived from the SI prefix kilo-) is a unit of information or computer storage equal to either 1024 or 1000 bytes. ...

Hardware description

Although the C128 could access more than 64KB of RAM through bank switching, the memory inside the REU could only be accessed by memory-transfers (STORE/LOAD/SWAP/COMPAREs) between the main memory and the REU memory, thus, giving an equivalent to a (slow) small memory window. Additionally, the C128's built-in BASIC 7.0 had three statements, STASH,FETCH, and SWAP, for storing and retrieving data from the REU. Bank switching (also known as paging, but unrelated to the ordinary meaning of this term in computing) was a technique common in 8-bit microcomputer systems, to increase the amount of addressable RAM and ROM without extending the address bus. ... Commodore BASIC is the dialect of BASIC used in Commodore Internationals 8-bit home computer line, stretching from the PET of 1977 to the C128 of 1985. ...

1764 REU with Utility Disk and 2.5 amp power supply

Officially, only the 1700 and 1750 were supported on the C128. The 256KB model, the 1764, was released for the C64 at the same time. However, aside from a bundled 2.5 amp C64 power supply unit (the factory unit could not support the 1764), there were only minor differences between the three models. Download high resolution version (800x602, 205 KB)Commodore 1764 REU with Utility Disk and 2. ... Download high resolution version (800x602, 205 KB)Commodore 1764 REU with Utility Disk and 2. ... Amp re can refer to: Amp re (car) Ampere (unit) Andr -Marie Amp re This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ...

In practice, the difference between the 1764 and the earlier units had little effect on compatibility, and people used 1700s and 1750s successfully with the C64, and 1764s successfully with the C128, although the C64's factory power supply was inadequate to reliably handle the power load of a 1700 or 1750. Some dealers unbundled the 1764 and the power supply in order to sell the power supply to C64 users.

Because of memory chip shortages in the late 1980s, the 1750 was only produced in small quantities. However, due to Commodore's longtime practice of filling unused chip sockets with solder, it was difficult to upgrade a 1700 or 1764 to 512K. Several firms did this commercially, either selling upgraded units or upgrading customer-supplied units. An integrated circuit (IC) is a thin chip consisting of at least two interconnected semiconductor devices, mainly transistors, as well as passive components like resistors. ...

In the early 1990s, DIY modification schemes to increase the capacity of a REU to one megabyte or higher appeared on various online services. See also: DIY Network, a cable TV network. ... This article is about a unit of data measurement. ...

Model differences

The 1700's circuit board was identical to that of the 1750, and a trace marked J1 indicated the size of the chips used. On the 1750 and 1764, this trace was cut. Close-up photo of one side of a motherboard PCB, showing conductive traces, vias and solder points for through-hole components on the opposite side. ...

The 1700 and 1750 had a resistor at position R4 that, according to Commodore engineer Fred Bowen, compensated for subtle differences in the expansion port on the C64 and C128. The 1764 lacked that resistor. Bowen and other CBM engineers recommended against using a 1764 with a C128 it unless the resistor was added, or a 1700/1750 with a C64 unless the resistor was removed. Resistor symbols A resistor is a two-terminal electrical component that creates an electrical potential difference across its terminals that is proportional to the current passing through it. ...

It was possible to check for the presence of a 1750 by reading memory address $DF00's bit 4, which was 1 on a 1750, and 0 on a 1700 or 1764. However, since this procedure would not distinguish between a 1700 and a 1764, many programmers wrote to the RAM itself to find out the amount of memory installed. In computer science, a memory address is a unique identifier for a memory location at which a CPU or other device can store a piece of data for later retrieval. ... This article is about the unit of information. ...

REU software support

Very little software made use of the REUs. Like other add-on products from Commodore, their relatively small installed base relative to the huge installed base of the C64 made software developers hesitant to invest much time and effort in supporting it, and the lack of commercial support kept sales lower than they otherwise might have been. Commodore is the commonly used name for Commodore International, a West Chester, Pennsylvania based electronics company who was a major player in the 1980s home computer field. ...

The REUs came with software to utilize the extra memory as a RAM disk, but the RAM disk's compatibility with commercial software was spotty, as some commercial software relied heavily on various quirks of the Commodore 1541 floppy drive. Additionally, many commercial programs simply overwrote the memory space occupied by the RAM disk software. A RAM disk or RAMdrive is a segment of active computer memory, RAM, which is being used as secondary storage, typically a role for a disk drive. ... The Commodore 1541 (originally called VIC-1541), made by Commodore Intl, was the best-known floppy disk drive for the Commodore 64 home computer. ...

The GEOS operating system had built in support for the REU as a RAM disk, as did the C128's version of CP/M, and some disk copy programs used the REU to facilitate high-speed copying with a single disk drive. GEOS as well as other programs even used the REU for quick memory transfers within the host machine's main memory by storing a memory block into the REU and then fetching it back to another location. Using this method, only the actual data to be transferred needed to travel on the machine's data bus—unlike the ordinary method, which had the computer's CPU do the transfer, thus spending bus capacity on instruction fetches as well as payload data. GEOS (Graphic Environment Operating System) was an operating system from Berkeley Softworks (later Geoworks). ... A RAM disk or RAMdrive is a segment of active computer memory, RAM, which is being used as secondary storage, typically a role for a disk drive. ... CP/M is an operating system created for Intel 8080/85 and Zilog Z80 based microcomputers by Gary Kildall of Digital Research, Inc. ... Primary storage is a category of computer storage, often called main memory. ... In computer architecture, a bus is a subsystem that transfers data or power between computer components inside a computer or between computers. ... This CPU uses numerous pins to connect to the motherboard. ... GEORGE IS FUCKING GAY ...

Due to its high speed relative to Commodore's floppy drives or even the commercially available hard drives, the REU also became popular with BBS operators. A bulletin board system or BBS is a computer system running software that allows users to dial into the system over a phone line and, using a terminal program, perform functions such as downloading software and data, uploading data, playing games, reading news, and exchanging messages with other users. ...

See also

• Super 1750 Clone
• geoRAM
• RAMLink