How does R compute sums of squares?

Consider the following missing data problem:

?y = c(1, 2, 2, 2, 3)
a = factor(c(1, 1, 1, 2, 2))
b = factor(c(1, 2, 3, 1, 2))
fit = lm(y ~ a + b)
anova(fit)

?Analysis of Variance Table

Response: y
? ? ? ? ?Df ?Sum Sq Mean Sq ? ?F value ? ?Pr(>F)
a ? ? ? ? ?1 0.83333 0.83333 1.3637e+33 < 2.2e-16 ***
b ? ? ? ? ?2 1.16667 0.58333 9.5461e+32 < 2.2e-16 ***
Residuals ?1 0.00000 0.00000
---
Signif. codes: ?0 ?***? 0.001 ?**? 0.01 ?*? 0.05 ?.? 0.1 ? ? 1
Warning message:
In anova.lm(fit) :
?ANOVA F-tests on an essentially perfect fit are unreliable

I am trying to understand how R computes sums of squares. I know that R
makes a FORTRAN call to dqrls to make a QR decomposition of the design
matrix, which returns (among other things),

?fit$effects
?(Intercept) ? ? ? ? ? ?a2 ? ? ? ? ? ?b2 ? ? ? ? ? ?b3
-4.472136e+00 ?9.128709e-01 ?7.715167e-01 ?7.559289e-01 ?2.471981e-17

Can anyone elaborate on how R computes these effects? I am not satisfied
with the explanation that R provides with the help(effects) command.

Thanks in advance.

Ethan

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