Better Understand of memory

Hi folks! i posted a forum in cpu section regarding on my motherboard and memory problem, but i think i found a solution with that and i wanna know something about my memory.

What im using right now is advance modules pc2100 ddr266 133mhz 512mb in conroe865GV using pentium D820, but when i use it on my older motherboard, ECS741gxm socket A motherboard, it appears 1Gig, just wanna know why it appears 1gig though its only 512mb??

here are some of the details of my memory:
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Logical/Chipset 1 Memory Banks
Bank 0 : 512MB DDR-SDRAM 2.5-4-4-8 (tCL-tRCD-tRP-tRAS) CR1
Channels : 1
Speed : 2x 133MHz (266MHz data rate)
Multiplier : 2/3x
Width : 64-bit
Memory Controller in Processor : No
Performance Acceleration Technology : No
Refresh Rate : 7.80µs
Power Save Mode : No
Fixed Hole Present : No

APIC 1
Version : 2.00
Multiplier : 1/2x
Maximum Interrupts : 24
IRQ Handler Engaged : Yes
Enhanced Support : Yes

Memory Module 1
Type : 512MB DDR-SDRAM
Technology : 8x(64Mx8)
Speed : PC2100U
Standard Timings : 2.5-3-3-6 (tCL-tRCD-tRP-tRAS)
Date of Manufacture : Saturday, December 25, 1999
Set Timing @ 133MHz : 2.5-3-3-6 (tCL-tRCD-tRP-tRAS)
Set Timing @ 100MHz : 2.0-2-2-5 (tCL-tRCD-tRP-tRAS)