Editing Conventional memory (section)

=== Additional memory ===
One technique used on early [[IBM XT]] computers was to install additional RAM into the video memory address range and push the limit up to the start of the [[Monochrome Display Adapter]] (MDA). Sometimes software or a custom [[address decoder]] was required for this to work. This moved the barrier to 704&nbsp;KB (with MDA/HGC) or 736&nbsp;KB (with CGA).<ref name="Atkinson"/><ref name="Paul_1997_NWDOSTIP"/>

[[DOS memory management|Memory manager]]s on [[Intel 80386|386-based]] systems (such as [[QEMM]] or MEMMAX (+V) in [[DR-DOS]]) could achieve the same effect, adding conventional memory at 640&nbsp;KB and moving the barrier to 704&nbsp;KB (up to segment B000, the start of MDA/HGC) or 736&nbsp;KB (up to segment B800, the start of the CGA).<ref name="Paul_1997_NWDOSTIP"/> Only CGA could be used in this situation, because [[Enhanced Graphics Adapter]] (EGA) video memory was immediately adjacent to the conventional memory area below the 640&nbsp;KB line; the same memory area could not be used both for the [[frame buffer]] of the video card and for transient programs.

All Computers' piggy-back add-on [[memory management unit]]s ''AllCard'' for XT-<ref name="Petzold_1986_Allcard"/><ref name="PCW_1986_AllCard"/> and ''Chargecard''<ref name="Zerbe_1987_AllCharge"/> for 286/386SX-class computers, as well as MicroWay<!--, Inc.-->'s ECM (Extended Conventional Memory) add-on-board<ref name="Petzold_1986_ECM"/> allowed normal memory to be mapped into the A0000–EFFFF ([[hexadecimal|hex]]) address range, giving up to 952&nbsp;KB for DOS programs. Programs such as [[Lotus 1-2-3]], which accessed video memory directly, needed to be [[patch (computing)|patched]] to handle this memory layout. Therefore, the 640&nbsp;KB barrier was removed at the cost of hardware compatibility.<ref name="Zerbe_1987_AllCharge"/>

{{anchor|Console redirection}}<!-- Redirecting here for now, as there is no better target. A standalone Console redirection article is needed. -->It was also possible to use '''console redirection'''<ref name="Kontron_2021"/> (either by specifying an alternative console device like [[AUX:]] when initially invoking [[COMMAND.COM]] or by using [[CTTY (DOS command)|CTTY]] later on) to direct output to and receive input from a [[dumb terminal]] or another computer running a [[terminal emulator]]. Assuming the [[System BIOS]] still permitted the machine to boot (which is often the case at least with BIOSes for embedded PCs), the video card in a so called [[headless computer]] could then be removed completely, and the system could provide a total of 960&nbsp;KB of continuous DOS memory for programs to load.

Similar usage was possible on many DOS- but not IBM-compatible computers with a non-fragmented memory layout, for example [[Seattle Computer Products|SCP]] [[S-100 bus]] systems equipped with their [[Intel 8086|8086]] CPU card CP-200B and up to sixteen SCP&nbsp;110A memory cards (with 64&nbsp;KB RAM on each of them) for a total of up to 1024 KB (without video card, but utilizing console redirection, and after mapping out the boot/BIOS ROM),<ref name="Paterson_2007_SCP"/> the [[Victor 9000]]/[[Sirius 1]] which supported up to 896&nbsp;KB, or the [[Apricot PC]]<!-- the figure for the Apricot PC is not currently known, except for that it was more than 640 KB --> with more continuous DOS memory to be used under its custom version of MS-DOS.