USB-Disk Module
3.0
AP-UMxxxxAUXXX-XXXTX
3
© 2015 Apacer Technology, Inc. Rev. 1.2
1. General Description
Apacer’s USB-Disk Module (UDM) is a high performance, embedded solid state drive (SSD) designed to
replace a conventional IDE hard disk drive. UDM SSD can be plugged into a standard Embedded USB
connector commonly found in desktops, portable PC systems and industrial PC systems. This product is
well suited for embedded flash storage applications offering new and expanded functionality as well as
more cost-effective designs, better performance and increased reliability.
1.1 Performance-optimized Controller
The heart of an UDM is the USB controller, which translates standard USB signals into the data and
controls of the flash media. This proprietary USB controller is specifically designed to attain high data
throughput from host to flash.
1.1.1 Error Correction Code (ECC)
The UDM uses BCH Error Detection Code (EDC) and Error Correction Code (ECC) algorithms which
correct up to 72bit random single-bit errors for each 1024-byte block of data depending on spare area of
flash memory. High performance is achieved through hardware-based error detection and correction.
1.1.2 Wear-Leveling
Flash memory can be erased a limited number of times, This number is called the erase cycle limit, or
write endurance limit, The erase cycle limit applies to each individual erase block in the flash device.
In a typical application, and especially if a file system is used, specific pages are constantly updated (e.g.,
the page that contains the FAT, registry, etc.). Without any special handling, these pages would wear out
more rapidly than other pages, reducing the lifetime of the entire flash.
To overcome this inherent deficiency, Apacer’s USB-Disk Module (UDM) uses wear-leveling algorithm.
This wear-leveling algorithm ensures that consecutive writes of a specific sector are not written physically
to the same page in the flash. This spreads flash media usage evenly across all pages, thereby
maximizing flash lifetime.
The wear-leveling mechanism provides write/erase cycles for reliable data storage over an extended
period.
