Atom Memory Details

Start Size Chip Type Hardware Software Details
0000 1K IC51,52 2114 Block zero RAM  
0400 1K     Teletext VDU RAM 0400-2700 are external bus accessed.
0800 1K     VDU CRT Controller  
0C00 5K     Free (External)  
2000 1K     Free (External)
2000-21FF Catalogue Buffer
2200-27FF Sequential File Buffers
2400 1K     Free (External)
2800 1K IC10,11 2114 User RAM
2800-28FF Floating Point Variables
2900-2FFF User program area
2C00 1K IC12,13 2114 User RAM
3000 1K IC14,15 2114 User RAM
3400 1K IC16,17 2114 User RAM
3800 1K IC18,19 2114 User RAM
3C00 1K     Free (External)
4000 16K     Free (External)
8000 1K IC42,43 2114 VDC Video RAM  
8400 1K IC40,41 2114 VDC Video RAM  
8800 1K IC38,39 2114 VDC Video RAM  
8C00 1K IC36,37 2114 VDC Video RAM  
9000 1K IC34,35 2114 VDC Video RAM  
9400 1K IC32,33 2114 VDC Video RAM  
9800 1K     Free (External)  
9C00 1K     Free (External)  
A000 4K IC24   Optional Utility ROM  
B000 1K IC25 8255 PPI  
B400 1K PL8   Expansion (internal)  
B800 1K IC1 6522 VIA  
BC00 1K     Free (internal) Good space for mapping a second 6522
C000 4K IC20   Atom BASIC  
D000 4K IC21   Optional Extension ROM  
E000 4K     Optional DOS ROM  
F000 4K IC20   Assembler & COS  

From the above, you can see that the Atom requires about 4K RAM to run.